What the evidence says. Several controlled trials; effects real but modest or context-dependent.
What is Lactobacillus casei Shirota?
Lactobacillus casei Shirota (Lacticaseibacillus paracasei Shirota (Yakult)) is a probiotic strain used for reduces antibiotic-associated diarrhoea and c. difficile-associated diarrhoea in hospitalised older adults (hickson 2007). NutriDex grades the human evidence as Moderate. Lacticaseibacillus paracasei (formerly Lactobacillus casei) strain Shirota, the live culture in Yakult, is one of the most studied probiotic strains, almost always delivered as a fermented-milk drink rather than a capsule. Its best-supported use is preventing antibiotic-associated diarrhoea (AAD): the landmark Hickson 2007 BMJ trial cut AAD from 34% to 12% and C. difficile diarrhoea from 17% to 0% in hospitalised older adults, though a later rigorous spinal-cord-injury RCT (ECLISP) found no overall AAD benefit except in proton-pump-inhibitor users. Randomised trials also show modest, reproducible improvement in stool consistency and defecation frequency, reduced winter upper-respiratory-tract infections in office workers, and blunting of stress-related cortisol rise and abdominal symptoms in exam-stressed students. Effects are strain- and dose-specific and tend to be modest; results across indications are mixed rather than uniformly positive.
Purported Benefits
✓Reduces antibiotic-associated diarrhoea and C. difficile-associated diarrhoea in hospitalised older adults (Hickson 2007)
✓Lowers AAD risk in antibiotic-treated patients who regularly take proton-pump inhibitors (ECLISP subgroup)
✓Improves stool consistency and increases defecation frequency in people prone to constipation or with soft stools
✓Reduces the incidence and duration of winter upper-respiratory-tract infections in healthy adults
✓Blunts stress-induced salivary cortisol rise and relieves stress-associated abdominal symptoms under academic stress
Typically 6.5 x 10^9 to 1 x 10^11 (about 6.5 billion to 100 billion) live LcS cells once daily, taken as a fermented-milk drink. For AAD prevention, given once daily during the antibiotic course and continued ~7 days after; for regularity, respiratory and stress outcomes, daily intake over 4-12 weeks.
Active Compounds
Yakult / Yakult Light fermented-milk drink (~6.5-10 billion LcS per 65 mL bottle)Yakult 1000 / Y1000 (~100 billion LcS, marketed for stress and sleep)Strain designations: Lacticaseibacillus paracasei Shirota, L. casei strain Shirota (LcS), YIT 9029Almost exclusively a probiotic fermented-milk beverage rather than a capsule or powder
Safety & Cautions
⚠
Generally well tolerated; trials report no serious intervention-related adverse events, and a surveillance study in critically ill children found no LcS colonisation or bacteraemia. As with all live probiotics, use caution in critically ill, severely immunocompromised, or central-venous-catheter patients, in whom rare lactobacillus bacteraemia/endocarditis has been reported with the genus. The drink contains milk and added sugar (relevant for lactose intolerance and diabetes/glycaemic control). Probiotics do not replace standard treatment for active infection. Educational only — always check with your doctor or pharmacist before combining Lactobacillus casei Shirota with any medicine.
Common questions about Lactobacillus casei Shirota
What is Lactobacillus casei Shirota used for?
Lactobacillus casei Shirota is most often taken for Reduces antibiotic-associated diarrhoea and C. difficile-associated diarrhoea in hospitalised older adults (Hickson 2007), Lowers AAD risk in antibiotic-treated patients who regularly take proton-pump inhibitors (ECLISP subgroup), Improves stool consistency and increases defecation frequency in people prone to constipation or with soft stools, Reduces the incidence and duration of winter upper-respiratory-tract infections in healthy adults. The original Yakult strain — best evidence for preventing antibiotic-associated diarrhoea and supporting bowel regularity
Does Lactobacillus casei Shirota work — what does the evidence say?
Moderate evidence. Several controlled trials; effects real but modest or context-dependent. Lacticaseibacillus paracasei (formerly Lactobacillus casei) strain Shirota, the live culture in Yakult, is one of the most studied probiotic strains, almost always delivered as a fermented-milk drink rather than a capsule. Its best-supported use is preventing antibiotic-associated diarrhoea (AAD): the landmark Hickson 2007 BMJ trial cut AAD from 34% to 12% and C. difficile diarrhoea from 17% to 0% in hospitalised older adults, though a later rigorous spinal-cord-injury RCT (ECLISP) found no overall AAD benefit except in proton-pump-inhibitor users. Randomised trials also show modest, reproducible improvement in stool consistency and defecation frequency, reduced winter upper-respiratory-tract infections in office workers, and blunting of stress-related cortisol rise and abdominal symptoms in exam-stressed students. Effects are strain- and dose-specific and tend to be modest; results across indications are mixed rather than uniformly positive.
What is the typical dose of Lactobacillus casei Shirota?
Typically 6.5 x 10^9 to 1 x 10^11 (about 6.5 billion to 100 billion) live LcS cells once daily, taken as a fermented-milk drink. For AAD prevention, given once daily during the antibiotic course and continued ~7 days after; for regularity, respiratory and stress outcomes, daily intake over 4-12 weeks.
Is Lactobacillus casei Shirota safe? Any cautions or side effects?
Generally well tolerated; trials report no serious intervention-related adverse events, and a surveillance study in critically ill children found no LcS colonisation or bacteraemia. As with all live probiotics, use caution in critically ill, severely immunocompromised, or central-venous-catheter patients, in whom rare lactobacillus bacteraemia/endocarditis has been reported with the genus. The drink contains milk and added sugar (relevant for lactose intolerance and diabetes/glycaemic control). Probiotics do not replace standard treatment for active infection.
How many studies support Lactobacillus casei Shirota?
NutriDex cites 10 sources for Lactobacillus casei Shirota, graded "Moderate".
Cite this page
APA
Peh, D. (2026). Lactobacillus casei Shirota (Lacticaseibacillus paracasei Shirota (Yakult)): Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 16 Sept 2026, from https://nutridex.info/s/l-casei-shirota
BibTeX
@misc{nutridex_l_casei_shirota,
author = {Peh, Daryl},
title = {Lactobacillus casei Shirota (Lacticaseibacillus paracasei Shirota (Yakult)): Benefits, Dosage, Side Effects \& Evidence},
year = {2026},
howpublished = {NutriDex --- The Supplement Research Compendium},
url = {https://nutridex.info/s/l-casei-shirota},
note = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-09-16}
}
For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.